FRANKFURT—A European Central Bank executive board member, in an interview with The Wall Street Journal, sent one of the clearest signals to date that the ECB is poised to embark on large-scale asset purchases early next year, as the bank grapples with a weak economy and dangerously low inflation.

ECB board member Benoît Coeuré also provided details of the ECB’s plans to publish minutes of its policy meetings starting next year, saying the accounts should be released four weeks after meetings and will be “substantial” in providing...